
\ 



UNITED STATES COAST SURVEY. 



DIRECTIONS 



OBSERVATIONS OF TIDES. 



FREWTEM* FOR VIEE USE OF TIME VEEt.EE ORSERVERS FROM 
TEEE JfE^JTEJSCREJPr EJVSVREJCTEOJYS, 1852. 



Gideon & Go ; Printers. 



L 



r 



UNITED STATES COAST SUKVEY. 



DIRECTIONS 



OBSERVATIONS OF TIDES. 



PRIJYTEB FOR TBE USE OF VBF TJB^JL OBSERVERS FRO. 11 
TBE JfT^JTUSCRIPT EJTSTRWJCVIOJYS, 1852. 



Gideon & Co. ; Printers. 



i 



' > 



\V- \ 






<P 







^ 



INSTRUCTIONS 



FOR OBSERVERS OF TIDES EMPLOYED BY THE U. S. COAST SURVEY. 



H 



The tidal stations are either permanent (for the year) 
or temporary. The object of the permanent stations is 
to determine with precision the establishment, rise and fall, 
and duration of tides, and the effect upon them of atmos- 
pheric and other circumstances, so as to form a tide table, 
or one for the prediction of tides at the place. The com* 
parison of the precise results thus obtained at suitable 
points of the coast, will give the progress of the tide wave. 
(Genl. Hydrog. Instruc, 1845, Par. 19.) 

There are certain tidal stations established for the spe- 
cial purpose of determining the progress of the tide wave 
by observations of a short period, where all the precautions 
should be taken as at a permanent station. 

INSTRUCTIONS FOR OBSERVERS AT PERMANENT TIDAL STATIONS OB- 
SERVING HIGH AND LOW WATER ONLY. 

Tide Gauge. 

1. The gauge should, when practicable, be of the form 
called the box gauge, having a copper float, a wooden rod 
graduated to feet and tenths, and reading by a vernier, or 
by estimation, to hundredths 5 graduated so that greater 
readings correspond to rise of tide and smaller to fall 
The holes admitting the water to the box should be nu~ 
merous enough and large enough to admit it freely, but not 
to permit oscillation. A slide should be provided which 
will enable the observer to cover a greater or less number 
of these holes, so as to vary the facility of access of the 
water to the gauge under different circumstances of wind, 
&c. 



In establishing the gauge, care should be taken that, at 
the lowest water to be observed, there is still at least six 
inches under the float, and that the highest range possible 
is attainable by the marks on the staff. 

If the situation will not allow a box gauge, a simple 
staff, graduated upwards, and reading to feet and tenths, 
may be firmly planted, and observed directly or through a 
small telescope from a distance of twenty or thirty feet. 

A permanent mark, corresponding to the zero of the 
tide staff, should be made near the gauge ; a copper nail, 
the centre of the head corresponding to the zero, and 
surrounded by a circle of nails of the same material, or a 
line cut into a stone ; or the zero should be referred by 
the difference of level to some permanent mark, as the 
plinth of a light-house, or the corner-stone of some adja- 
cent building. 

The highest or lowest tide known in the vicinity, its 
date and circumstances, should be recorded. 

Observations, 

2. High and low water must be observed both night and 
day; the time, and the height, and the interval of slack- 
water being carefully ascertained. 

About twenty minutes before the time of high water, 
and ten minutes after, the observations must be made 
every two minutes, and must be recorded, whether the 
reading is the same or varies. 

The time should be mean solar time. The watch used 
should be corrected daily, when the sun shines, by a mark 
furnished by the chief of the hydrograpbic party estab- 
lishing the tidal station, or to be otherwise procured, when 
this resource fails, for the sun's meridian passage, and an 
almanac, or extract from one, showing the equation of 



time to be applied, and whether additive or subtractive, to 
convert apparent solar time into mean solar or clock time, 

3. Besides the observations of rise and fall of tide, me- 
teorological observations are required, including those of 
the barometer, thermometer, hygrometer, and of the di- 
rection and force of the wind, for which special instruc- 
tions will be given. 

Records. 

4. The observer will be furnished with printed forms for 
his records. The original to be kept in a bound volume, 
the duplicate on loose sheets. He should, from day to 
day, make a copy of his observations on the loose sheets, 
and at the end of each month send them to the Coast 
Survey office, and on the acknowledgment of their re- 
ceipt send the original. 

The packages sent are to be placed in a cover addressed 
" Coast Survey Office, Washington, D. C ,-" over which a 
second cover is to be placed addressed " Hon. Thomas 
Corwin, Secretary of the Treasury, Washington, D. C; " 
on each cover, in the upper right hand corner, is to be 
written "Official Business." 

The original and duplicate must be commenced by a 
description of the gauge, stating its form, dimensions, 
graduations, &c, the points to which its zero is referred, 
a sketch of the locality where it is placed, and notes of 
the general character of the place in reference to sur- 
rounding objects. Especially the influence which the 
position is likely to have in retarding the tide wave, or 
preventing or augmenting its rise, or the effect of winds in 
raising or depressing the water, and on the time of high 
or low water. 

The mark of reference must be carefully described. The 
date of observations and names of the tidal observers must 



appear on the face of the record, and all blanks in the 
forms be filled up. 

The time of high and low water should have written 
opposite to them in the column of remarks, "H." and "L." 
water, and the time of slack water, (when there is no rise 
or fall,) should be noted below. 

Remarks. 

5. Observers cannot be too careful to note the facts pre- 
cisely as they occur, without regard to what may seem to 
them to be the regular succession of heights and of times. 
What appear to be irregularities are frequently most im- 
portant phenomena. Any attempt to force the observa- 
tions, will, when detected by a comparison of results or 
otherwise, deprive the observer at once of employment. 

If an observation is accidentally omitted, its place should 
be left blank, and allowances will be made for such omis- 
sions, unless frequent, or the result of carelessness. 

Negligence should be reported at once to the officer in 
charge of the station, or, when there is no one in special 
charge, to the office. 

The observers will remark, that the observations of the 
night tides are a& essential as those of the day tides. 

Meteorological observations. 

6. The directions of the wind are to be observed to the 
nearest points ; an easy moving vane being mounted for 
that purpose on a tall pole, with a small flag as a check, 
and a circle divided below. 

The circle is to be made on a stick of timber fixed firmly 
in the ground, and divided like the mariner's compass into 
points and half points. 

In the centre of the circle the pole with the flag is to 
be placed. The observer, in making the observations, has 



7 

only to notice the direction in which the vane is blown, 
and, referring to the stationary compass, notice the direc- 
tion of the wind. 

The force of the wind is to be recorded according to the 
scale, as follows: 

Table of force of winds. 

Velocity in miles per hour. 

0. Calm - - - . o 

1. Light air ------ 1 

2. Light breeze ----- 4 

3. Moderate breeze - 13 

4. Fresh breeze ----- 23 

5. Strong breeze ----- 32 

6. Fresh gale 40 

7. Strong gale 50 

8. Whole gale 60 

9. Storm 80 

10. Hurricane 100 

7. The mean time to be given by a mark to be placed as 
above stated ; by which, and an almanac to be furnished 
to the observers for the equation of time, they will regu- 
late their watches. 

8. The height of the barometer, and temperature by 
attached thermometer, to be noted when the tides are 
observed. 

The temperature, by a thermometer in the air, and 
carefully screened from reflected or radiated heat, to be 
observed at the same time. 

The temperature of the wet bulb thermometer to be 
also observed. 

Description and use of the " Alexander barometer" 

9. The following is a description of the mode of mount- 
ing and using the Alexander barometer, which has been 
furnished to most of the tidal stations : 



This barometer, as made by Mr. James Green, of New 
York, consists essentially of an iron cup or cistern I, sup- 
ported by a metal bracket E, (see the annexed sketch,) and 
containing mercury, in which is immersed the barometer 
tube, B, sustained at the upper end by a metal clamp and 
hook, o and /, and attached to the wall by means of the 
metal bracket F ; a scale of inches and tenths is marked 
upon the tube, on which slides a vernier, L, reading to 
hundredths, the zero of the graduation being a line marked 
upon the tube near its lower extremity. A small iron 
socket, g-, having in it a single hole, which can be closed 
by the screw, c, is firmly attached to the lower end of the 
tube. An ivory float, K, is made to fit loosely around the 
barometer tube, and allowed to rest upon the surface, a &, 
of the mercury in the cistern, it being easier for the eye 
to note the coincidence of an ivory edge than a mercurial 
surface with the zero line. The nut, G, serves to raise or 
lower the tube at pleasure. 

When the barometer is to be set up, the tube filled with 
mercury, and closed at the lower extremity by the screw, 
c, is taken from the case carefully inverted, and, with the 
lower end immersed in the cup or cistern of mercury, is 
held in that position until the ivory float and moveable 
vernier can be slipped round it, and the metal hook clamped 
to its upper extremity ; the finger is then carefully inserted 
beneath the mercurial surface, and the screw taken out — 
slowly, so that the mercury in the tube may fall gradually 
to its proper height. The vernier is then adjusted to the 
scale, and the instrument is ready for use. 

In taking down the barometer, the ivory float, the ver- 
nier, and the metallic hook by which the tube is suspen- 
ded, are first detached from it. The tube is then carefully 
inclined, its lower extremity being kept immersed in the 
mercury until the fluid rises to the top and completely fills 



9 

the tube. The small screw is then inserted in the orifice, 
and the barometer being removed from the cistern is in- 
verted and placed in its leathern case, which is so contrived 
that the tube hangs in it suspended from its metallic socket. 
The diameter of the tube is about one-sixth of an inch. 

The reading of the barometer is noted by first making 
the edge of the ivory float coincide with the zero mark on 
the tube. This is effected by means of a screw, H, inserted 
underneath the iron cistern, and working in a metal support, 
so that the cup of mercury, and with it the float, can be 
elevated or depressed at pleasure. Supposing this done, 
we proceed to observe the height of the summit of the 
column. Take hold of the tube with the left hand so that 
it may retain as closely as possible its vertical position, and 
tap slightly upon it near the top of the column ; this breaks 
any adherence which may have taken place between the 
mercury and the glass. Then move the slide, M, which 
carries the vernier, until the plane, passing through its zero, 
is tangent to the top of the convex surface of the mercurial 
column. It is well to have a screen of white paper placed 
behind the barometer to assist the eye in determining when 
the meniscus thus formed is perfect, that is, when the 
summit of the column and the edge of the slide just touch 
each other, leaving no line of light between. Before read- 
ing it, it is better to allow the barometer to remain at rest 
a few moments, and then note whether the zero line still 
remains tangent to the convex surface, and whether the 
edge of the float still coincides with the zero of the scale. 
If these adjustments still continue exact, the inches and 
tenths are then read off from the scale, and the hundredths 
from the vernier. 

10. A small thermometer should be attached to the 
tube, and the bulb of another be allowed to dip in the cup 
of mercury, by which the temperatures of the tube and 
of the mercury may be noted. 
2 



10 

For the mode of placing the thermometer to give the 
temperature of the air, of reading and verifying, see the 
directions for meteorological observations by the Smith- 
sonian Institution .* 

11. The same directions are to be followed in regard 
to placing, observing and verifying, the wet bulb ther- 
mometer, the rain and snow gauges, the character of the 
sky and of the clouds. The direction and force of the 
wind, however, will be observed and recorded as already 
stated in these instructions. 

12. Those observers to whom the Smithsonian barom- 
eters have been furnished should follow the same instruc- 
tions for using that instrument. 

INSTRUCTIONS FOR OBSERVERS AT PERMANENT TIDAL STATIONS 
OBSERVING HOURLY. 

13. To the requirements in the foregoing instructions 
are added observations hourly during the day and night. 

When the rise and fall of the tide is small, as in the 
Gulf of Mexico, the observations near the times of high 
and low water need not be taken more frequently than 
every fifteen minutes ; and where the time of occurrence 
of high and low water is irregular, so that there are 
sometimes two high and two low waters, and at other 
times there is only one high and one low water, in the 
twenty-four hours, regular half hourly observations are to 
be preferred to any attempt to determine more minutely 
the time of high and low water. 

When hourly tidal observations are made, the barometer 
and attached thermometer, the detached thermometer, 
with dry and wet bulb, and other meteorological instru- 
ments, will be observed at the times and according to the 

* Directions for meteorological observations, intended for the first class of observers, 1850. 



11 

rules given in the instructions of the Smithsonian Insti- 
tution in the chapter entitled " Time of observations." 
The direction and force of the wind, and general character 
of the weather, will be recorded every hour. The scale 
to be used for the force of wind is that given in these 
instructions. 



THE END. 



THE ALEXANDER hAKOMKTKK 



D 



V„ - X 



AI.KXAXDKH KAHOMKTKK 



£■ 



I- J 



• Mi. ;pn /. 



i 



\ 



LIBRARY OF CONGRESS 



a' 029 ivTzsF™ 



